EP3477390A1 - Inspektionswerkzeug, lithographische vorrichtung, elektronenstrahlquelle und inspektionsverfahren - Google Patents

Inspektionswerkzeug, lithographische vorrichtung, elektronenstrahlquelle und inspektionsverfahren Download PDF

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Publication number
EP3477390A1
EP3477390A1 EP17198202.8A EP17198202A EP3477390A1 EP 3477390 A1 EP3477390 A1 EP 3477390A1 EP 17198202 A EP17198202 A EP 17198202A EP 3477390 A1 EP3477390 A1 EP 3477390A1
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EP
European Patent Office
Prior art keywords
electron beam
sample
polarization state
substrate
response signal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP17198202.8A
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English (en)
French (fr)
Inventor
Erwin Paul Smakman
Albertus Victor Gerardus MANGNUS
Thomas Jarik HUISMAN
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ASML Netherlands BV
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ASML Netherlands BV
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Publication date
Application filed by ASML Netherlands BV filed Critical ASML Netherlands BV
Priority to EP17198202.8A priority Critical patent/EP3477390A1/de
Priority to US16/652,231 priority patent/US11243179B2/en
Priority to JP2020514189A priority patent/JP7134226B2/ja
Priority to PCT/EP2018/076639 priority patent/WO2019081162A1/en
Priority to TW107136447A priority patent/TWI708936B/zh
Publication of EP3477390A1 publication Critical patent/EP3477390A1/de
Priority to IL274051A priority patent/IL274051B2/en
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70605—Workpiece metrology
    • G03F7/70616—Monitoring the printed patterns
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B15/00—Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
    • G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
    • G01N23/2251—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion using incident electron beams, e.g. scanning electron microscopy [SEM]
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70691—Handling of masks or workpieces
    • G03F7/70716—Stages
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/06—Electron sources; Electron guns
    • H01J37/065—Construction of guns or parts thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/06—Electron sources; Electron guns
    • H01J37/073—Electron guns using field emission, photo emission, or secondary emission electron sources
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/22—Optical or photographic arrangements associated with the tube
    • H01J37/222—Image processing arrangements associated with the tube
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2210/00—Aspects not specifically covered by any group under G01B, e.g. of wheel alignment, caliper-like sensors
    • G01B2210/56—Measuring geometric parameters of semiconductor structures, e.g. profile, critical dimensions or trench depth
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2223/00—Investigating materials by wave or particle radiation
    • G01N2223/60—Specific applications or type of materials
    • G01N2223/611—Specific applications or type of materials patterned objects; electronic devices
    • G01N2223/6116—Specific applications or type of materials patterned objects; electronic devices semiconductor wafer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
    • G01N23/225—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material using electron or ion
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/06—Sources
    • H01J2237/063—Electron sources
    • H01J2237/06308—Thermionic sources
    • H01J2237/06316—Schottky emission
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/245—Detection characterised by the variable being measured
    • H01J2237/24507—Intensity, dose or other characteristics of particle beams or electromagnetic radiation
    • H01J2237/24557—Spin polarisation (particles)
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/26—Electron or ion microscopes
    • H01J2237/28—Scanning microscopes
    • H01J2237/2813—Scanning microscopes characterised by the application
    • H01J2237/2814—Measurement of surface topography
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/26—Electron or ion microscopes
    • H01J2237/28—Scanning microscopes
    • H01J2237/2813—Scanning microscopes characterised by the application
    • H01J2237/2817—Pattern inspection

Definitions

  • the present invention relates to an inspection tool, a lithographic apparatus, an electron beam source and an inspection method.
  • a lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate.
  • a lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs).
  • a patterning device which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC.
  • This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate.
  • resist radiation-sensitive material
  • a single substrate will contain a network of adjacent target portions that are successively patterned.
  • Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the "scanning"-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
  • the radiation beam as typically applied in lithographic apparatuses may e.g. be a DUV radiation beam (e.g. having a wavelength of 248 nm or 193 nm) or an EUV radiation beam (e.g. having a wavelength of 11 nm or 13.5 nm).
  • a DUV radiation beam e.g. having a wavelength of 248 nm or 193 nm
  • EUV radiation beam e.g. having a wavelength of 11 nm or 13.5 nm.
  • the manufacturing of an integrated circuit may typically require the stacking of a plurality of layers, whereby the layers need to be accurately aligned. Without such an alignment, a required connection between layers may be flawed, resulting in a malfunctioning of the integrated circuit.
  • the bottom layer or layers of the integrated circuit will contain the smallest structures, such as transistors or components thereof.
  • the structures of subsequent layers are typically larger and enable connections of the structures in the bottom layers to the outside world. In view of this, an alignment of two layers will be the most challenging in the bottom portion of the integrated circuit.
  • substrates are often subjected to inspection, using inspection tools such as e-beam inspection tools.
  • An example of such an inspection tool is a high resolution SEM (scanning electron microscope), which is e.g. used to examine dimensions of patterns on a substrate.
  • a high resolution SEM typically uses electrons, with an energy between 200 eV and 30 keV, which are accelerated towards the surface of the substrate, where they diffuse into and generate new electrons (i.e. secondary electrons). Due to this, secondary and/or backscattered electrons are emitted from the surface. These secondary and/or backscattered electrons may then be recorded by a detector. By scanning an area of a substrate using a beam of electrons, information about the surface structure of the substrate can be obtained.
  • an inspection method for a substrate comprising:
  • an inspection tool comprising:
  • an electron beam source comprising:
  • a lithographic apparatus comprising:
  • FIG. 1 schematically depicts a lithographic apparatus according to one embodiment of the invention.
  • the apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or any other suitable radiation), a mask support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioning device PM configured to accurately position the patterning device in accordance with certain parameters.
  • the apparatus also includes a substrate table (e.g. a wafer table) WT or "substrate support" constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioning device PW configured to accurately position the substrate in accordance with certain parameters.
  • a radiation beam B e.g. UV radiation or any other suitable radiation
  • a mask support structure e.g. a mask table
  • MT constructed to support a patterning device (e.g. a mask) MA and connected to a
  • the apparatus further includes a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W.
  • a projection system e.g. a refractive projection lens system
  • PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W.
  • the illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.
  • optical components such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.
  • the mask support structure supports, i.e. bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment.
  • the mask support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device.
  • the mask support structure may be a frame or a table, for example, which may be fixed or movable as required.
  • the mask support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms "reticle” or “mask” herein may be considered synonymous with the more general term "patterning device.”
  • patterning device used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
  • the patterning device may be transmissive or reflective.
  • Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels.
  • Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types.
  • An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.
  • projection system used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”.
  • the apparatus is of a transmissive type (e.g. employing a transmissive mask).
  • the apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask)
  • the lithographic apparatus may be of a type having two (dual stage) or more substrate tables or “substrate supports” (and/or two or more mask tables or “mask supports”).
  • substrate tables or “substrate supports” and/or two or more mask tables or “mask supports”
  • additional tables or supports may be used in parallel, or preparatory steps may be carried out on one or more tables or supports while one or more other tables or supports are being used for exposure.
  • the lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate.
  • a liquid having a relatively high refractive index e.g. water
  • An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques can be used to increase the numerical aperture of projection systems.
  • immersion as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that a liquid is located between the projection system and the substrate during exposure.
  • the illuminator IL receives a radiation beam from a radiation source SO.
  • the source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD including, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp.
  • the source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.
  • the illuminator IL may include an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as ⁇ -outer and ⁇ -inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted.
  • the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.
  • the radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the mask support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W.
  • the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B.
  • the first positioning device PM and another position sensor can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan.
  • movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioning device PM.
  • movement of the substrate table WT or "substrate support" may be realized using a long-stroke module and a short-stroke module, which form part of the second positioning device PW.
  • the mask table MT may be connected to a short-stroke actuator only, or may be fixed.
  • Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks PI, P2.
  • the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks).
  • the mask alignment marks may be located between the dies.
  • the depicted apparatus could be used in at least one of the following modes:
  • the lithographic apparatus further comprises an inspection tool IT according to the invention.
  • an inspection tool IT may e.g. enable to determine a characteristic of a structure, in particular a buried structure that is present on or in an area of interest of a substrate W that is processed by the lithographic apparatus.
  • the inspection tool may comprise an electron beam source for inspecting the substrate.
  • the second positioning device PW may be configured to position the substrate W in the operating range of the inspection tool IT.
  • the inspection tool IT may e.g. be configured to determine a characteristic of the mentioned structure, e.g. an electric characteristic, a material characteristic and/or a geometric characteristic.
  • this information may subsequently be provided to a control unit of the lithographic apparatus and used during the exposure process, e.g. by controlling one or more of the illumination system, the projection system or one of the positioning devices, based on the information.
  • the lithographic apparatus may be configured to apply DUV radiation for the radiation beam.
  • the patterning device MA may be a transmissive patterning device and the projection system PS may comprise one or more lenses.
  • the lithographic apparatus may be configured to apply EUV radiation for the radiation beam.
  • the patterning device MA may be a reflective patterning device and the projection system PS may comprise one or more mirrors.
  • the apparatus may comprise one or more vacuum chambers for housing the illumination system IL and/or the projection system PS.
  • the lithographic apparatus may comprise an inspection tool according to the present invention, in order to perform an inline or offline inspection of a substrate that is to be processed or has been processed.
  • an inspection tool configured to inspect an object such as a semiconductor substrate.
  • Figure 2 schematically shows an embodiment of such an inspection tool 100.
  • the inspection tool 100 comprises an electron beam source 110, further on also referred to as an e-beam source 110.
  • an e-beam source 110 is known in general, and may be applied in the present invention to project an electron beam 120 onto an area of an object 130, e.g. a substrate.
  • the object 130 is mounted to an object table 132 by means of a clamping mechanism 134, e.g. a vacuum clamp or an electrostatic clamp.
  • the area of the object onto which the e-beam is projected may also be referred to as sample.
  • Such an e-beam source 110 may e.g. be used to generate an electron beam 120 having an energy ranging from 0.2 keV to 100 keV.
  • An e-beam source 110 may typically have one or more lenses for focusing the electron beam 120 onto a spot of about 0.4 to 5 nm in diameter.
  • the e-beam source 110 may further comprise one or more scanning coils or deflector plates which may deflect the electron beam 120. By doing so, the electron beam 120 may e.g.
  • the electron beam source is configured to project a plurality of electron beams onto a respective plurality of sub-areas of the area of interest. By doing so, the area of interest that can be examined or inspected per unit of time may be enlarged. Further, in an embodiment of the present invention, the electron beam source may be configured to generate electron beams having a different energy level.
  • the inspection tool further comprises a control unit 170 or processing unit, e.g. comprising a microprocessor, computer or the like, for processing the emitted secondary or back-scattering electrons as detected by the detectors 150 and 151.
  • a control unit 170 or processing unit e.g. comprising a microprocessor, computer or the like, for processing the emitted secondary or back-scattering electrons as detected by the detectors 150 and 151.
  • control unit 170 comprises an input terminal 172 for receiving signals 152 from the detectors 150, 151, the signals 152 representing the detected emitted secondary or back-scattering electrons.
  • control unit may further have an output terminal 174 for outputting a control signal 112 for controlling the e-beam source 110.
  • control unit 170 may control the e-beam source 110 to project an e-beam 120 onto an area of interest of the object to be inspected, e.g. a semiconductor substrate.
  • control unit 170 may be configured to control the e-beam source 110 to scan the area of interest.
  • the detector may receive secondary or back-scattering electrons 140 from different portions of the area of interest.
  • the applied e-beam may e.g. have a cross-section of 1 - 4 nm in diameter, while the area of interest is 100 nm x 100 nm.
  • a response to the e-beam across the area of interest may have been captured by detectors 150, 151, where the detected signal is comprised of detected electrons per illuminated pixel.
  • the pixel size may be e.g. be smaller or larger than the cross-section of the e-beam.
  • Figure 3 highly schematically shows a cross-sectional view of a semiconductor structure 400 comprising multiple layers and different materials.
  • the structure 400 as schematically shown in Figure 3 comprises a bottom layer 402 of a first material, and a top layer 408 of a second material, the second layer having a change in topology, in particular an increased height, when propagating along the X-direction.
  • Figure 3 further schematically shows an e-beam 410 impinging on the top surface 412 of the structure 400. Indicated by the dotted line 414 is the interaction volume of the e-beam 410, i.e. the volume where secondary or back-scattering electrons may be generated as a result of the applied e-beam.
  • FIG. 3 schematically shows a detector signal I as detected during a scan of the electron beam 410 along the X-direction.
  • a detector signal I as detected during a scan of the electron beam 410 along the X-direction.
  • a decrease 450 occurs in the detector signal I
  • a brief increase 460 occurs.
  • the occurrence of such a variation of the detector signal I may thus be used to determine a position of a height step in a layer of a sample.
  • a spin-polarized electron beam for the inspection of a semiconductor sample. It is proposed to spin-polarize the electron beam, by using the intrinsic magnetic moment of electrons, and applying such an e-beam to inspect a sample. It is believed, as will be explained in more detail below, that such an approach may result in several improvements of known SEM-based inspection tools, such as high resolution SEMs. In particular, it is expected that the following improvements can be realised:
  • Figure 4 schematically shows the interaction volume 414 as generated by an unpolarized e-beam 410 when impacting a surface 412.
  • the interaction volume 414 can be considered to be the result of a first interaction volume 414.1 which is primarily occupied with electrons having a negative spin polarization, indicated as ⁇ - , and a second interaction volume 414.2 which is primarily occupied with electrons having a positive spin polarization, indicated as ⁇ + .
  • ⁇ + a first interaction volume 414.1 which is primarily occupied with electrons having a negative spin polarization
  • ⁇ + a positive spin polarization
  • Figure 5(a) left side of the figure, illustrated the interaction volume 514 (-) underneath a surface 412 when an electron beam 510 (-), an electron beam with a negative spin polarization ⁇ - , impacts the surface 412
  • Figure 5(b) right side of the figure, illustrated the interaction volume 514 (+) underneath a surface 412 when an electron beam 510 (+), an electron beam with a positive spin polarization ⁇ + , impacts the surface 412.
  • the spin-polarization of the incident electrons their interaction volume can be controlled.
  • the inventors believe that the spin-orbit coupling results in spin-selective scattering, which introduces the assymetry in the interaction volume.
  • This assymetric interaction volume may enable an increase in the spatial resolution in the following ways:
  • an inspection method for a substrate comprising the following steps:
  • a polarized state of an electron beam refers to the electron beam being spin-polarized to a certain degree.
  • the electron beam as applied to inspect the sample has a degree of spin-polarization p of at least 10 %. In a preferred embodiment, the degree of spin-polarization of the applied electron beam is 30-50 %.
  • the interaction volume is reduced in size.
  • the width of the interaction volume i.e. the size of the interaction volume in the X-direction, of a spin-polarized beam is smaller that the width of the interaction volume of an unpolarized beam.
  • the inspection method can e.g. be applied to determine geometric properties such as dimensions of structures on the surface of the substrate.
  • a line width of a structure may e.g. be determined in this manner, with an improved resolution.
  • geometric features of structures on a semiconductor substrate may be determined.
  • the inspection method is in particular applied to a semiconductor substrate for the inspection of structures on the surface of such a semiconductor substrate.
  • a semiconductor substrate for the inspection of structures on the surface of such a semiconductor substrate.
  • an inspection method that applies at least two consecutive electron beams to a sample that is to be inspected, whereby the two electron beams have a different polarization state.
  • Such an inspection method may e.g. comprise the following steps:
  • Figure 6 schematically illustrates the scanning by an electron beam of three different geometric structures, whereby these structures are scanned by an electron beam with a negative spin-polarization, indicated as ⁇ - , an electron beam with a positive spin-polarization, indicated as ⁇ + , and an electron beam with a unpolarized state, indicated as 'unpolarized'.
  • Graphs (a) to (i) illustrate a detector signal as can be obtained when the different geometric structures as scanned using the three different electron beams.
  • graphs (a) to (c) illustrate a detector signal that can be obtained when a substantially horizontal surface 612 is scanned.
  • Graphs (d) to (f) illustrate a detector signal that can be obtained when a slanted or sloped surface 614 is scanned.
  • Graphs (g) to (i) illustrate a detector signal that can be obtained when surface 616 with a height step, in particular a decrease in height, is scanned.
  • the detector signal as obtained using the three different electron beams i.e. ⁇ - , ⁇ + , and 'unpolarized', result in substantially similar detector signals.
  • the detector signals may e.g. be normalised to take account of differences in intensities of the applied electron beams.
  • the detector signal as obtained using the three different electron beams i.e. ⁇ - , ⁇ + , and 'unpolarized', result in different detector signals.
  • This can be attributed to the fact that the three different electron beams scan the surface with different interaction volumes, as illustrated in Figures 4 and 5 .
  • the surface 614 that is scanned has a slope. In the arrangement as shown, the surface 614 can be considered to have a negative slope.
  • Such a negative slope results in a comparatively small detector signal when the surface is scanned with the electron beam with the negative spin-polarization, indicated as ⁇ - .
  • This can be explained when considering that back-scattering and secondary electrons that are generated in the interaction volume of an electron beam with a negative spin-polarization, e.g. volume 514 (-) as shown in Figure 5 , are more remote from the surface 614 than back-scattering and secondary electrons that are generated in the interaction volume of an electron beam with a positive spin-polarization, e.g. volume 514 (+) as shown in Figure 5 .
  • the electrons may on average be closer or further away from the tilted surface.
  • the detector signal obtained by the negative spin-polarized electron beam will be lower than the detector signal obtained by the positive spin-polarized electron beam or by the unpolarized electron beam.
  • the surface that is scanned is slanted. It may also be mentioned that, the steeper the slope of the slanted surface, the larger the difference between the detector signals generated by the three different electron beams, i.e. ⁇ - , ⁇ - , and 'unpolarized', will be.
  • the present invention enables to make such a distinction by inspecting the surface with at least two electron beams with a different polarization state. Using an embodiment of the present invention, both the direction and magnitude of the slope may be identified.
  • Graphs (g) to (i) illustrate a detector signal that can be obtained when surface 616 with a height step is scanned.
  • a height step also affects the detector signal of the three different electron beams, i.e. ⁇ - , ⁇ - , and 'unpolarized', in a different manner.
  • a negative height step is scanned by an electron beam
  • a brief increase or peak 660 in the detector signal can be observed when scanning close to the height step, whereas, when the e-beam has passed the negative height step, a brief decrease or dip 650 may occur.
  • both the peak 660 and the dip 650 can be affected, due to asymmetric interaction volume that may occur in such circumstances.
  • the brief dip 660 occurring when the electron beam approaches the height step will be smaller when a negative spin-polarized electron beam is applied and will be larger when a positive spin-polarized electron beam is applied.
  • the use of a spin-polarized electron beam enable to control the shape of the interaction volume depending on the spin-polarization. This allows to modify how a geometry is measured, e.g. by a high resolution SEM.
  • a key geometry for which a high resolution SEM is typically employed, is to observe edges, i.e. height steps, of structures, see the third geometry presented in Figure 6 .
  • the detector signal will show an increase in signal at one side of the edge, while a reduction of the signal may be perceived at the other side of the edge.
  • This effect comes from the fact that the electrons near an edge can not only escape from the top surface, but also from the side of the edge, also called edge blooming.
  • By controlling or reshaping the interaction volume using a spin-polarized electron beam) such that it interacts with the edge in a limited way ( - in Figure 6 ), a less pronounced peak and a more pronounced dip in the signal. The opposite holds when using the opposite spin polarization ( + in Figure 6 ).
  • the sensitivity of the edge can be tuned by tuning the applied degree of spin-polarization, allowing for increasing the sensitivity of CD (critical dimension) measurements.
  • contributions from the flat surface to the signals can be removed.
  • Such contributions coming from the flat surface would typically be considered background offset or noise.
  • the signal-to-noise ratio of a high resolution SEM can be increased.
  • this allows for the reduction of measurement time per area. Or in other words, this allows for a throughput increase of the technique.
  • the present invention provides in an inspection method for inspecting a sample using an electron beam have a polarized state.
  • an inspection tool that is configured to perform the inspection methods according to the present invention.
  • an inspection tool according to the present invention may comprise the following components:
  • the e-beam source as applied may be configured to generate an e-beam having a first polarization state and an e-beam having a second polarization state.
  • the first polarization state and the second polarization state may e.g. be any combination of the three polarization states ⁇ - , ⁇ + , and 'unpolarized' as described.
  • a spin-polarized electron beam may e.g. be generated by illuminating a GaAs cathode with a circularly polarized infrared laser.
  • the inspection tool comprises a spin-polarized electron beam source comprising a GaAs cathode and an IR laser configured to emit a circularly polarized laser beam onto the cathode.
  • an alternative electron beam source which can be applied in an inspection tool according to the present invention.
  • the electron beam source according to the present invention applies a Schottky emitter.
  • a standard high resolution SEM Schottky emitter may be applied.
  • a standard Schottky emitter typically consists of a tungsten (W) core with a ZrO 2 thin film and operates around 1800 K. At this temperature many high-energy electrons are created that are extracted from the material with an electric acceleration field.
  • the ZrO 2 has the special characteristic that it lowers the work function at higher temperatures, which is beneficial for the extraction of electrons and thus for the maximum brightness and current that can be generated. This temperature at the same time slowly melts the ZrO 2 , which then distributes over the W surface. This is needed because otherwise the ZrO 2 would disappear in time from the W core through outgassing, degrading the electron beam source, in particular the Schottky emitter.
  • a modified Schottky emitter is proposed, the modified Schottky emitter enabling the generation of a spin-polarized electron beam.
  • a magnetic metallic coating or layer to the emitter. By doing so, the emitted electron beam can be spin-polarized. It can however be noted that there is however no metal that is still ferromagnetic at 1800 K. The highest Curie (transition temperature) is for Co at 1388 K, another candidate would be Fe with a Curie temperature of 1043 K. In order to avoid lowering the operating temperature of the Schottky emitter (and therefore diminishing the output brightness and current), it is proposed to rely on the paramagnetic properties of the materials instead. In order to magnetize the metallic coating or layer that is applied to the emitter, an external magnetic field can be applied. Such external magnetic field can magnetize the metallic layer and can thus create a spin barrier for the electrons that polarizes the electron beam. In a preferred embodiment, Fe is used for the metallic layer, because of its high magnetic susceptibility.
  • FIG. 7 schematically shows an embodiment of the modified Schottky emitter which can be used in an inspection tool.
  • a conventional Schottky emitter 710 is schematically shown, the emitter 710 having a tip shaped W core 720 provided with a ZrO 2 coating 730.
  • the Schottky emitter 710 may generate an electron beam 740, whereby the polarization of the electrons of the beam, indicated by the arrows 750, have no preferred direction.
  • the generated electron beam 740 can be considered to be unpolarized or in an unpolarized state.
  • a modified Schottky emitter 800 according to an embodiment of the present invention is schematically shown.
  • the modified Schottky emitter 800 has a tip shaped W core 820 provided with a ZrO 2 coating 830.
  • the emitter 800 further comprises a metallic coating 840, e.g. an iron or ferrous coating.
  • a metallic coating 840 e.g. an iron or ferrous coating.
  • the external magnetic field may be generated by one or more current carrying coils.
  • Such coils may e.g. be arranged in the vicinity of the emitter 800, enabling the magnetization of the metallic layer 840.
  • the one or more coils may be mounted to a magnetic yoke such as a ferromagnetic yoke, for guiding the magnetic flux to the emitter 800.
  • the use of one or more coils for generating the external magnetic field provided the advantage that the magnetic field strength is easily adjusted. By e.g. reversing the current to the coil or coils, one can reverse the external magnetic field and thus reverse the spin-polarization of the electron beam 860.
  • permanent magnets may also be applied to generate the external magnetic field 850.
  • Such permanent magnets may also be mounted to a magnetic yoke such as a ferromagnetic yoke, for guiding the magnetic flux to the emitter 800.
  • the relative position of the permanent magnets and the emitter 800 can be made adjustable, e.g. by means of a positioning device such as an actuator.
  • FIG 8 schematically depict a more detailed embodiment of an inspection tool 200 according to the present invention.
  • the inspection tool 200 comprises an e-beam source, referred to as the electron gun 210 and an imaging system 240.
  • the electron gun 210 comprises an electron source 212, a suppressor electrode 214, an anode 216, a set of apertures 218, and a condenser 220.
  • the electron source 212 can be a Schottky emitter or modified Schottky emitter as discussed above.
  • the electron beam 202 can be extracted, and the electron beam 202 may be controlled by using a tunable aperture 218 which may have different aperture sizes for eliminating the unnecessary electron beam outside of the aperture.
  • the condenser 220 is applied to the electron beam 202, which also provides magnification.
  • the condenser 220 shown in the figure 2 may e.g. be an electrostatic lens which can condense the electron beam 202.
  • the condenser 220 can be also a magnetic lens.
  • the imaging system 240 may e.g. comprise a blanker 248, a set of apertures 242, a detector 244, four sets of deflectors 250, 252, 254, and 256, a pair of coils 262, a yoke 260, and an electrode 270.
  • the electrode 270 is used to retard and deflect the electron beam 202, and further has electrostatic lens function due to the combination of upper pole piece and sample 300.
  • the coil 262 and the yoke 260 are configured to the magnetic objective lens.
  • the deflectors 250 and 256 can be applied to scan the electron beam 202 to a large field of view, and the deflectors 252 and 254 can be used for scanning the electron beam 202 to a small field of view. All the deflectors 250, 252, 254, and 256 can control the scanning direction of the electron beam 202.
  • the deflectors 250, 252, 254, and 256 can be electrostatic deflectors or magnetic deflectors.
  • the opening of the yoke 260 is faced to the sample 300, which immerses the magnetic field into the sample 300.
  • the electrode 270 is placed beneath the opening of the yoke 260, and therefore the sample 300 will not be damaged.
  • the retarder 270, the sample 300, and the upper pole piece form a lens to eliminate the chromatic aberration of the electron beam 202.
  • lithographic apparatus in the manufacture of ICs
  • the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc.
  • LCDs liquid-crystal displays
  • any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or "target portion”, respectively.
  • the substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.
  • imprint lithography a topography in a patterning device defines the pattern created on a substrate.
  • the topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof.
  • the patterning device is moved out of the resist leaving a pattern in it after the resist is cured.
  • UV radiation e.g. having a wavelength of or about 365, 248, 193, 157 or 126 nm
  • EUV radiation e.g. having a wavelength in the range of 5-20 nm
  • particle beams such as ion beams or electron beams.
  • lens may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.
  • the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein.
  • a data storage medium e.g. semiconductor memory, magnetic or optical disk

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EP17198202.8A 2017-10-25 2017-10-25 Inspektionswerkzeug, lithographische vorrichtung, elektronenstrahlquelle und inspektionsverfahren Withdrawn EP3477390A1 (de)

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EP17198202.8A EP3477390A1 (de) 2017-10-25 2017-10-25 Inspektionswerkzeug, lithographische vorrichtung, elektronenstrahlquelle und inspektionsverfahren
US16/652,231 US11243179B2 (en) 2017-10-25 2018-10-01 Inspection tool, lithographic apparatus, electron beam source and an inspection method
JP2020514189A JP7134226B2 (ja) 2017-10-25 2018-10-01 検査ツール、リソグラフィ装置、電子ビーム源、及び検査方法
PCT/EP2018/076639 WO2019081162A1 (en) 2017-10-25 2018-10-01 INSPECTION TOOL, LITHOGRAPHIC APPARATUS, ELECTRON BEAM SOURCE, AND INSPECTION METHOD
TW107136447A TWI708936B (zh) 2017-10-25 2018-10-17 檢測工具、微影裝置、電子束源與檢測方法
IL274051A IL274051B2 (en) 2017-10-25 2020-04-19 Test tool, lithographic apparatus, electron beam source and test method

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TW201923340A (zh) 2019-06-16
JP7134226B2 (ja) 2022-09-09
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